1. Field of the Invention
The invention relates to an auto document feeder. More specifically, an auto document feeder with a sensor device capable of recognizing the characteristic of a sheet and that the sheet is present in a feeding path or not.
2. The Related Art
According to the progress of the image processing technology, many image processing products are popularly used, such as printers, scanners, fax machines, copy machines, etc. According to processing a large amount of documents, an auto document feeder is developed for cooperating with image processing products described above.
The auto document feeder can catch one sheet from a stack of the document and transfers the sheet to the image processing products continuously. Therefore, the image processing products can uninterrupted process a large amount of document without feeding the sheet to the image processing products manually.
A conventional auto document feeder 900 is shown in FIG. 6 and FIG. 7. The auto document feeder 900 cooperates with an image processing product (not shown in figures) and has a base 901 and a frame 902 mounted on the base 901, which defines a feeding path 903. One end of the feed path 903 is arranged a first sensor device 904 mounted on the base 901, and the other end of the feeding path 903 is arranged a second sensor device 905 mounted on the frame 902.
The first sensor device 904 detects material of a sheet (not shown in figures) fed into the feeding path 903 and sends a signal to a processing circuit (not shown in figures) for adjusting operation of sheet processing according to the signal. While different sheets are fed into the feeding path 903, the first sensor device 904 can send different signals to the processing circuit corresponding to the different sheets. The processing circuit therefore adjusts operation of sheet processing, according to the different signals.
The second sensor device 905 has a detecting module 906 and a swing module 907. The swing module 907 has a shaft 908, a first swing arm 909 extending from the shaft 908 in one of radial direction of the shaft 908 and a second swing arm 910 extending from the shaft 908 in another one radiating direction of the shaft 908.
While the swing module 907 mounted on the frame 902, a spring 911 interconnects between the frame 902 and the swing module 907. The swing module 907 is hitched on the frame 902 by the spring 911. The first swing arm 909 of the swing module 907 is located in the feeding path 903 and the second swing arm 910 of the swing module 907 is located to corresponding to the detecting module 906 mounted on the frame 902.
While the sheet is fed into the feeding path 903 and passed through the swing module 907, the sheet pushes the first swing arm 909 of the swing module 907. Therefore, the first swing arm 909 of the swing module 907 is shifted an angle and the second swing arm 910 is shafted same angle together with the first swing arm 909. The detecting module 906 detects shift of the second swing arm 910 of the swing module 907 and sends a signal to the processing circuit to recognize that the sheet is fed into the feeding path.
However, the conventional auto document feeder 900 has a first sensor device 904 and a second sensor device 905 for recognizing material of the sheet and recognizing that the sheet is present in the feeding path 903 or not. Therefore, the cost of the conventional auto document feeder 900 is increased and the structure of the conventional auto document feeder 900 is complex.
While the conventional auto document feeder 900 is shook, the swing module 907 of the second sensor device 905 is moved. While the detecting module 906 detects shift of the second swing arm 910 of the swing module 907 caused by shaking the conventional auto document feeder 900, the detecting module 906 may erroneously recognize that the sheet is fed into the feeding path 903.